1. Field of the Invention
This invention relates to a method for reducing the generation of noise during arc welding by means of alternating current with welding machines with clocked current sources
U.S. Pat. Nos. 4,876,433; 4,371,776; 4,038,515 and German DE 38 16 238 Al disclose different embodiments of clocked, regulated welding energy sources which are suitable for welding with alternating current or for pulse welding and which provide reversible polarity.
In these known welding energy sources, the current set value is not changed, beginning with the polarization change request, as a function of time, resulting in the generation of considerable noise during welding
Only a few years ago, it was the goal of the manufacturers of welding machines, for example, ac-TIG welding machines, to generate a shape of the current flow as rectangular as possible at the time of the polarization change of the output current or the welding current flow.
However, the disadvantage of such a rectangularshaped welding current is considerable noise pollution. A welding arc of an ionized gas flow is subjected to the magnetic fields of the welding current and the gas molecules follow the changes of the magnetic field almost inertialess. This, in essence, constitutes a loudspeaker with a gas diaphragm. It is known to split a rectangular flow in accordance with Fourier into base and upper oscillations. Consequently, the rectangular-shaped flow of the welding arc emits a sonic frequency mixture rich in upper tones and thus is very loud.
In present-day inverter machines, it is possible to set the steepness of the current flow at the time of polarization change by means of the size of the output choke. Thus, maximum steepness is calculated from di/dl -U/L, where U is the maximally possible initial voltage and L is the inductance of the output choke. It is indeed possible to make the output current flow more trapezoidal using a choke with large inductance Such a flow generates fewer upper tones and thus the welding noise is reduced. However, the great disadvantage of this method is that it automatically negatively affects the dynamics of the current source. It also limits the maximally possible polarization change frequency at the output and greatly changes the shape of the curves of the welding current with different alternating frequencies.
Other known methods utilize additional filters to reduce the higher frequency portions in the output circuit in order to minimize noise. However, it should be noted that this requires condensers and chokes which must be designed for the full welding current and, therefore, are necessarily expensive. The disadvantages of these methods arise from the fact that it is only possible to use a few passive components and thus only a few, special curve shapes of the welding current can be generated. By adding filters, the dynamics of the current regulation are negatively affected. In addition, a passive filter has the corner values fixed by the components, while the alternating frequency of the welding current can change considerably.
Clearly, the noise level generated by ac-welding machines constitutes an essential environmental factor for people who must work every day with or next to them.